1. Field of the Invention
The present invention relates to a hydraulic valve timing apparatus which adjusts the timing of the opening and closing operation of either or both of an intake valve and an exhaust valve of an internal combustion engine, called the engine later on.
2. Discussion of Background
There has been known that when a camshaft is driven by a timing pulley or a chain sprocket rotating in synchronization with a crankshaft of the engine, a vane type valve timing mechanism can be provided between the timing pulley and the camshaft to relatively rotate the camshaft with respect to the crankshaft, and the rotation of the camshaft with respect to the rotation of the crankshaft is retarded or advanced to shift the operating timing of an intake valve or an exhaust valve with respect to the engine speed so as to reduce exhaust gas or improve fuel consumption, as disclosed in JP-A-192504, JP-A-7238815, JP-A-913920 and so on.
As disclosed in e.g. JP-A-960508, there has also been known that a stopper piston urged by a spring is provided in a vane rotor and a stopper hole which the stopper piston is engaged with is formed in a housing assembly wherein when oil pressure has not reached a predetermined pressure as e.g. just after starting the engine, the stopper piston is engaged with the stopper hole to prevent collision between the housing assembly and a vane, and when the oil pressure has reached the predetermined pressure, partial pressure of the oil pressure which is supplied to a retarding hydraulic chamber or an advancing hydraulic chamber through the vane rotor is used to move the stopper piston for release from the engagement with the stopper hole.
Since the conventional hydraulic valve timing adjusting apparatus as discussed above have the stopper piston and the spring provided in the vane rotor, the stopper piston is required to be housed in the vane rotor, in particular, in a vane so as to be slidable therein, reducing the strength of the vane.
Such arrangement could shift the center of gravity of the vane rotor to deform the vane rotor. If the clearance between the housing and the vane rotor become small in order to improve a sealing property, the vane rotor could contact with the housing.
Because a hydraulic chamber which moves the stopper piston using the oil pressure in the retarding hydraulic chamber and a hydraulic chamber which moves the stopper piston using the advancing hydraulic chamber are independently provided, a wasteful space has been required.
Since the hydraulic chamber which moves the stopper piston using the oil pressure in the retarding hydraulic chamber moves the spring using the difference in pressure receiving area caused by the difference between a large diameter portion and a small diameter portion of the stopper piston, it has been impossible to effectively use the oil pressure for movement of the stopper piston.